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1994 200hp Mercury 2.5 EFI XRi Switchbox

I have a 1994 200hp Mercury 2.5 EFI XRi with oil injection removed that has around 800 hours on it. It would not rev up while under load so I took it in to have it diagnosed to determine the problem. Shop has checked out the entire electrical/engine control and has diagnosed a bad switchbox for the port bank of cylinders. None of the cylinders on the port side were firing and they swapped switchboxes and it replicated the problem on the starboard side. So I am confident that I need to replace the switchbox. So here is my question for those that have more experience with this then I do.

1. Should I purchase a factory Mercury switchbox or do the aftermarket ones work just as well?
2. Would you trust a used factory switchbox from a used parts dealer.
2. Is there anything that needs to be done when changing out the switchbox other then just removing the old one and wiring up the new one? I would prefer to complete the repair myself and I have lots of mechanical experience I just did not have the tools to diagnosis the problem.

This motor is in great condition and has always run fine (until now). Never been in salt water and is almost exclusively used on inland lakes (so I am not really worried about being stranded offshore with it).

First, you have to replace both at the same time. ALWAYS!!. Second, there are many good aftermarket brands, CDI is common. And I'm not sure I'd buy used electrical parts. Especially since switchboxes MUST be replaced as pairs. I have no idea what 2 that have been on different engines would do, but I don't think I'd chance it.JMNSHO

like he says "change both"... lotta guys like cdi for fishin' type motors (production)... can buy 'em on ebay for touch over a hunred bucks a pair.. A10 and 12 replacements.. tha A number really makes no difference ona production motor other than $$$... jmo

I don't think 800 hours is that high. I have seen outboard boats used in ski school applications with 2000 hours on them without being rebuilt. It has never been rebuilt and is completely original except for the removal of the oil injection. The starboard bank has 132 to 135 psi and the port bank has 126 to 128 psi. The port side has been that low since I purchased the boat 8 years ago. The mechanic that did the diagnostic work on it was shocked at how clean all the electronics were under the flywheel and questioned whether it had ever been replaced. The motor has never been in salt water and is always cleaned and covered after use. All I have had to do is rebuild the water pump, rebuild the fuel pump, change the fuel filter and change the gear oil. This is all done annually and this motor has never left me stranded.

It is on a Barefoot ski boat that has been used for competitive training. This means lots of engine run time in the 4000 to 5000 RPM range for slower speed shoe ski training as well as higher speed almost WOT runs for training on my bare feet. It has a 19 pitch high five prop on it and runs 45 mph trimmed all the way down at WOT and it will get there fast enough to throw you out of the spotters seat if you are not hanging on when I hit it. I believe that part of the longevity of the motor has to do with the removal of the oil injection. While oil injecting is nice for convenience I believe that it is harder on the motor and adds another place for catastrophic failure.

This is an older photo of the boat from right after I purchased it. It still looks the same except for the prop that I have on it now.